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Permalink Reply by Jason Haeger on February 2, 2010 at 1:33pm

This may be too vague of a topic starter to get much of a response.

I suggest a title change to: "Does the puck swell?"

It'll get people thinking in the right direction.

That having been said, I do think that the puck swells. ;)

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Permalink Reply by Mike Sabol on February 2, 2010 at 3:23pm

I think a viscous mass with convection currents is formed. The shape of the basket and the condition/size/shape of the holes would support/inhibit various convection currents that could be benificial/detremental to the extraction of the coffee.

I think someone at MIT should set up a super-computer simulation of espresso extraction.

There you go.

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Permalink Reply by Jason Shipley on February 2, 2010 at 5:40pm

The puck has to swell or at least wants to. Look at how coffee reacts when you brew in a pour over or press. I'd wonder weather it could expand up against the water and if it was fully constrained by the sides and bottom of the basket. So extraction happens against the coffees natural state, it wants to swell and absorb the water but is constrained by the pressure of the water from above and the portafilter basket. My best guess would be that the puck only swells up towards the gouphead after pressure from the water stops and the coffee is able to absorb some of the water remaining in the basket.

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Permalink Reply by Jason Haeger on February 2, 2010 at 5:50pm

Ding Ding Ding!

At least, that's been my theory for a number of years.

Jason Shipley said:

The puck has to swell or at least wants to. Look at how coffee reacts when you brew in a pour over or press. I'd wonder weather it could expand up against the water and if it was fully constrained by the sides and bottom of the basket. So extraction happens against the coffees natural state, it wants to swell and absorb the water but is constrained by the pressure of the water from above and the portafilter basket. My best guess would be that the puck only swells up towards the gouphead after pressure from the water stops and the coffee is able to absorb some of the water remaining in the basket.

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Permalink Reply by Brady on February 2, 2010 at 5:51pm

Jason Haeger said:

This may be too vague of a topic starter to get much of a response.

I suggest a title change to: "Does the puck swell?"

It'll get people thinking in the right direction.

That having been said, I do think that the puck swells. ;)

Yes... the title on its own is pretty vague. However I thought, in the context of the discussion that people seemed to want to have on the other thread (but not wanting to derail things) I'd give it another place to go...

I may bring some of those responses over to create a bit more context. Until then...

I too believe that the puck swells. If it were "sucked up against the screen" there'd probably be a void in the spent puck... most of mine are pretty solid.

On another note...

In a discussion on extraction that we had here a couple of months ago, Lem Butler shared the idea that an important part of the extraction process was the compression of the grounds. He suggested that it was similar to pressing out oils from other seeds, olives, etc. He felt that for this to occur, your basket must be filled to at least a certain level - enough so that the growth caused by the puck would be held back and force a sort of "self compression".

I'd not heard this. Still not quite sure what to think of it. Thoughts?

The guys also discussed the impact of the processing method, roast, and other bean factors on portafilter behavior. Some coffees are more hydrophyllic than others... they'll absorb more water and as a result grow more during extraction. This effects the compression effect... in a given basket, a higher dose would be necessary of a relatively hydrophobic coffee as compared to a hydrophyllic one. We pulled identical doses of 3 different coffees - dried, washed, and natural, and observed varying degrees of puck integrity and "muddyness". We also observed the differences in the flavor of the "muddy puck" coffee once the dose had been increased to reach the "proper degree of compression". (For science's sake, this probably should have been followed by a set of shots pulled with the same dose using a deeper basket, to eliminate that variable.)

Ok... not much but its a start.

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Permalink Reply by Jason Haeger on February 2, 2010 at 5:57pm

On the topic of hydrophilia, vs. hydrophobia. I'm inclined to agree.

I've often found myself frustrated at not being able to get a full extraction from SL28 beans ever, regardless of brew method.



Brady said:

Jason Haeger said:

This may be too vague of a topic starter to get much of a response.

I suggest a title change to: "Does the puck swell?"

It'll get people thinking in the right direction.

That having been said, I do think that the puck swells. ;)

Yes... the title on its own is pretty vague. However I thought, in the context of the discussion that people seemed to want to have on the other thread (but not wanting to derail things) I'd give it another place to go...

I may bring some of those responses over to create a bit more context. Until then...

I too believe that the puck swells. If it were "sucked up against the screen" there'd probably be a void in the spent puck... most of mine are pretty solid.

On another note...

In a discussion on extraction that we had here a couple of months ago, Lem Butler shared the idea that an important part of the extraction process was the compression of the grounds. He suggested that it was similar to pressing out oils from other seeds, olives, etc. He felt that for this to occur, your basket must be filled to at least a certain level - enough so that the growth caused by the puck would be held back and force a sort of "self compression".

I'd not heard this. Still not quite sure what to think of it. Thoughts?

The guys also discussed the impact of the processing method, roast, and other bean factors on portafilter behavior. Some coffees are more hydrophyllic than others... they'll absorb more water and as a result grow more during extraction. This effects the compression effect... in a given basket, a higher dose would be necessary of a relatively hydrophobic coffee as compared to a hydrophyllic one. We pulled identical doses of 3 different coffees - dried, washed, and natural, and observed varying degrees of puck integrity and "muddyness". We also observed the differences in the flavor of the "muddy puck" coffee once the dose had been increased to reach the "proper degree of compression". (For science's sake, this probably should have been followed by a set of shots pulled with the same dose using a deeper basket, to eliminate that variable.)

Ok... not much but its a start.

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Permalink Reply by Brady on February 2, 2010 at 6:43pm

Jason Shipley said:

The puck has to swell or at least wants to. Look at how coffee reacts when you brew in a pour over or press. I'd wonder weather it could expand up against the water and if it was fully constrained by the sides and bottom of the basket. So extraction happens against the coffees natural state, it wants to swell and absorb the water but is constrained by the pressure of the water from above and the portafilter basket. My best guess would be that the puck only swells up towards the gouphead after pressure from the water stops and the coffee is able to absorb some of the water remaining in the basket.

Interesting thought.

The thing I think is relevant for that question is that, once the basket contains only water and grounds (no air), the water pressure will act omni-directionally. (Assuming I remember Fluid Dynamics correctly). This means that if you were to measure the pressure at any point in the middle of the puck, the pressure at that point acts from all directions. It is the "static pressure" of the fluid.

The water is clearly being moved from top to bottom, but the speed is so slow that both the "dynamic pressure" and drag force pulling the grinds down are both minimal. I guess what I'm saying is that I don't believe that there is actually anything pushing the puck down. This leads me to think that it will attempt to expand in all directions equally, even during extraction.

Thoughts?

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Permalink Reply by Bryan Wray on February 2, 2010 at 9:07pm

I don't really have anything to add that hasn't been mentioned already, but I'm really going to enjoy reading this thread. Thanks Brady.

-bry

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Permalink Reply by Alex on February 3, 2010 at 12:57am

I've always beieved that when hot water enters the basket, the aroma and warmth attracts tiny angels who then begin massaging the coffee granules, coaxing the oils and flavours out before being carried through the basket and into the cup with the flow of water.

Nobody knows for sure why the angels do it; I think they may be junkies who are doing nothing but trying to get at and bath in the caffiene, but nobody has seen these angels, let-alone study them, so it really is a matter of pure speculation.

Bryan Wray said:

I don't really have anything to add that hasn't been mentioned already, but I'm really going to enjoy reading this thread. Thanks Brady. -bry

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Permalink Reply by Brady on February 3, 2010 at 5:23am

Mike Sabol said:

I think a viscous mass with convection currents is formed. The shape of the basket and the condition/size/shape of the holes would support/inhibit various convection currents that could be benificial/detremental to the extraction of the coffee.

I think someone at MIT should set up a super-computer simulation of espresso extraction.

There you go.

That's an interesting thought - that the puck could be a viscous fluid. I guess I'd always pictured the puck as mostly fused together and stationary. That could be happening, though I think it'd be more likely in a basket that was slightly under-filled, where there was more room for things to move around a bit.

I'd think that in a basket where the puck had swelled to meet the screen the whole puck would almost lock together, but have nothing concrete to base this on. Is reducing this effect one of the benefits of minimizing headspace?

Anybody have any connections in the fluid dynamics department of a local university?

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Permalink Reply by Brady on February 3, 2010 at 5:34am

Mike Sabol said:

... I think someone at MIT should set up a super-computer simulation of espresso extraction.

You know, we could probably get a little bit of a look into what is happening by mixing some ground-size "marker particles" (glitter?) in with the coffee. See where they end up once the whole thing is done?

Though this would be a great excuse to play with nano-bots, so I'm going to recommend that route instead.

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Permalink Reply by Jason Haeger on February 3, 2010 at 6:14am

My guess: They would end up towards the top.

I have a lot that I want to add, but not enough time to write it out. I hope to be back with more time later.

Brady said:

Mike Sabol said:

... I think someone at MIT should set up a super-computer simulation of espresso extraction.

You know, we could probably get a little bit of a look into what is happening by mixing some ground-size "marker particles" (glitter?) in with the coffee. See where they end up once the whole thing is done?

Though this would be a great excuse to play with nano-bots, so I'm going to recommend that route instead.

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